This invention relates to a system and method for aligning the eyes of a subject.
There are a number of situations where the alignment of a subject's eyes are important. The subject may be human or may be a research animal.
When taking certain types of eye measurements, one may need to know that the eye alignment is in a particular reference position. For example, if one measures the cornea of a person's eye before some type of treatment and one wishes to repeat those measurements after the treatment to determine how much, if any, the treatment has affected the measurements, one must ensure that the eye alignment is in the same position each time the particular measurements are made. Otherwise, the difference in data from before and after the treatment might be due to a change in eye alignment rather than the treatment.
In addition to those situations where one needs to ensure that eye alignment is in the same position for two or more different measurements, there are situations where eye alignment is desirable for diagnostic measurements of eye performance. There are situations when a human subject can simply be requested to fixate on a particular object. Thus, the human may state that he is currently looking at a light source, thereby providing "subjective" eye alignment information. However, there are situations where a doctor or researcher would like "objective" eye alignment information indicating the orientation of the eye and, to the extent possible, indicating what the eye is viewing. For example, very young children cannot be relied upon to fixate on such an object for measurements, such as refraction measurements which are very desirable to ensure that "in focus" images are being received when the child's brain is learning to interpret images. Likewise, adults subjected to extended eye examinations may become tired or subject to other duress and fail to maintain reliable fixation. A patient who is subjected to a therapeutic process such as laser ablation eye surgery may not be able to maintain desired eye orientation over an extended treatment time because of applied anesthesia, fatigue, or distraction by the procedure. Further, a research animal usually cannot be trained to fixate during eye measurements.
In each of the above cases, the failure or inability of the subject to maintain eye fixation upon an object can produce eye measurements or treatments that are seriously in error.
Therefore, there are situations where absolute eye alignment data is needed (i.e., the eye is aligned in a certain manner) and situations where comparative eye alignment data (i.e., the eye is in the same alignment as when earlier measurements were taken) are needed and one cannot rely upon a subject maintaining the alignment.
The use of various optical/electronic systems for making eye measurements has become more common in recent years. One example of such a system is shown in U.S. Pat. No. 4,213,678 to Pomerantzeff and Webb issued on Jul. 22, 1980. That patent discloses a scanning laser ophthalmoscope (SLO) for scanning a portion of the eye fundus. That patent, coinvented by one of the present inventors, is hereby incorporated by reference.